1. Field of the Invention
The present invention relates to a charging control in an IP Multimedia Subsystem (IMS).
2. Description of the Related Art
In IMS, an S-CSCF (Serving Call Session Control Function), AS (Application Server) and MRFC (Media Resource Function Processor) are the entities that are able to perform online charging. The AS and MRFC use an Ro reference point, while the S-CSCF uses an IMS Service Control (ISC) reference point for communicating with an Online Charging System (OCS) or ISC is terminated to IMS GW (GateWay) which uses Ro reference point to OCS as shown in FIG. 1.
A Session Charging Function (SCF) is intended to perform charging according to session resource usage, based on received requests from the S-CSCF/IMS GW via the ISC/Ro reference point. The SCF should be able to control session establishment by allowing or denying a session establishment request after checking the user's account. In addition, the SCF should be able to terminate an existing session when ‘the user's account is empty.
Flexible network usage, i.e. combining CS (Circuit Switched), PS (Packet Switched) and IMS networks/systems and related services and handovers, increases charging complexity. This may cause overlapping or double charging. Currently the overlapping charging cannot be avoided. The discarding of overlapping charging can partly be done in a post-processing system if common charging ID is available.
A private extension to SIP in the form of P-Charging-Function-Addresses and P-Charging-Vector headers is known. The former header is used to pass addresses of entities that provide a charging function. The latter header is used to pass charging correlation information. The affected UAs and proxies associated with a dialog or standalone transaction need to know the identities or addresses of the appropriate charging entities. They also need to pass correlation information so that the records generated and sent to the charging entities may be properly associated for a coordinated billing effort.